The present invention relates to a switching device suitable as a release switch for cameras.
Micro switches and leaf switches using a leaf spring are commonly used as a release switch for cameras. Recently, however, release switches arranged in such a manner that a dome-shaped spring made of a conductive material is fixed on a flexible circuit board as a release contact piece and the conducting portion formed on the flexible circuit board is brought into contact with the dome-shaped release contact piece by a release button to effect release operation have become widely used because their manufacturing cost is inexpensive.
FIG. 1 shows the typical arrangement of such a release switch. In FIG. 1, the release switch arrangement comprises a release button 2 serving as an operation button slidably attached to an upper cover 1, an elastically deformable dome-shaped release contact piece 3, a flexible circuit board 4, a member 5 by which the release contact piece 3 is fixed to the flexible circuit board 4, another contact piece 6 for actuating a light measuring device (not shown) interposed between the release contact piece 3 and the release button 2, a conducting portion 7 formed on the flexible circuit board 4 just below the release contact piece 3, and a mother plate 8 for supporting the flexible circuit board 4. The release button 2 includes a large diameter head portion 21, a small diameter shaft portion 22, and an enlarged diameter contact portion 23 disposed at the extreme end of the shaft portion 22, opposite to the head portion 21. A coil spring 9 surrounding the shaft portion 22 is interposed between the head portion 21 and a recessed surface 11 of the upper cover 1. In addition, a lock washer 24 is attached to the contact portion 23. With this arrangement, the release button 2 is neutrally urged to the outward direction of the upper cover 1 (kept at the position projecting from the upper cover 1) and the stroke of the release button 2 is also kept constant.
In the release switch arranged as described above, when the release button 2 is depressed, first, the contact portion 23 at the extreme end of the release button 2 is brought into contact with the another contact piece 6, and then with the dome-shaped release contact piece 3. When the release button 2 is further depressed, the release contact piece 3 is elastically deformed and brought into contact with the conducting potion 7 on the flexible circuit board 4 disposed just below it, whereby release operation is effected.
The release switch arranged as described above provides a so-called feeling of clicking in the release operation and thus provides a good feeling for the operation.
With the arrangement of the conventional release switch, however, there is a disadvantage as follows: when the release button is completely depressed, the extreme end 23 of the release button 2 is brought into contact while the mother plate 8 with nipping the release contact piece 3. The contact piece 6, and the conducting portion 7 of the flexible circuit board 4 therebetween, which causes a so-called feeling of collision against bottom. Further, since the mother plate is made of a rigid material, camera-shake occurs.
Further, there is a need for a switching device which does not cause the feeling of collision against the bottom in various fields in addition to being used as the release switch for cameras.